This comes despite continued opposition from many Sunnis and possible influence from outside Iraq.

Aides said the Shiite cleric would likely issue an official edict in the coming days. Any endorsement from al-Sistani could help garner the support of millions of faithful, but would likely have little influence on Kurdish and Sunni groups who have appeared more wary of the proposed constitution.

The news of al-Sistani’s support came a day after President Bush warned that violence in the war-torn nation would likely increase ahead of the scheduled Oct. 15 referendum.

“The number of attacks has increased, particularly in the last week, as the terrorists have begun their campaign to stop a referendum on the constitution,” Mr. Bush said Thursday. “They’ve had a history of escalating their attacks before Iraq’s major political milestones.”

And violence did continue on Friday when a suicide bomber killed at least five people in a car bombing and two American soldiers died in separate attacks.

The continued insurgency is part of what one regional leader, Saudi Foreign Minister Prince Saud al-Faisal, said Friday was a continuing trend toward disintegration in Iraq. Saud warned in an interview with journalists that Iraq still appeared to lack the political will to remain a single country and if the United States were to leave, the country could come apart.

“There is no dynamic now pulling the nation together,” he said. “All the dynamics are pulling the country apart.”

“I don’t think that a constitution by itself will resolve the issues, or an election by itself will solve the difficult problems.”

But Iraqi officials respond that many of the attacks are being fueled by neighboring states not doing enough to prevent insurgents from entering Iraq. In particular, the Iraqi government accused neighboring Syria of not doing enough to seal its border because it feared democratic reform.

Hoshyar Zebari, Iraq’s foreign minister, told the Associate Press in an interview, “It is important that the world should know, really, that Syria is not helping. It’s not cooperating, despite the many, many pledges, promises — none of that has happened.”

Zebari said that the Iraqi government was expecting attacks by insurgents who either entered Iraq from Syria or continued to use Syria as a base of operations would likely increase in the weeks leading up to the Oct. 15 referendum.

“They and others are frightened, really, of this experiment to succeed. This is the bottom line. They don’t want these values, these ideas to take root in a country like Iraq. This may affect them,” he said.

“I think this project of democracy-building in Iraq has alarmed many authoritarian autocratic regimes in the region,” Zebari said. “Many of them are counting on our failure, and they have not been helpful.”

Meanwhile, the debate over American involvement in Iraq was expected to be front and center this weekend in Washington, D.C. Opponents of the war expect some 100,000 people to gather near the White House on Saturday to call for the immediate withdrawal of U.S. soldiers from Iraq.

And advocates of leaving Iraq appeared to be gaining support among the general public. A CNN/USA Today/Gallup survey released Friday found that 55 percent of those surveyed said they wanted to see the United States intensify efforts to withdraw from Iraq, while 41 percent said they wanted no change in policy.

President Bush acknowledged the sentiment Thursday, but urged Americans to stay the course.

“Some Americans want us to withdraw our troops so that we can escape the violence,” the president said. “I recognize their good intentions, but their position is wrong. Withdrawing our troops would make the world more dangerous and make America less safe.”

In an effort to bolster support, those backing the president planned a series of counter-protests for the weekend in an effort to rally more Americans to the administration’s side.

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